The present invention relates to novel toner agents in general and, in particular, to metal-containing complexes usable in toners for developing electrostatic images in electrophotography, electrostatic recording, electrostatic printing, etc.
Conventional processes for converting latent electrostatic images to visible images are generally divided into two groups: liquid developing processes which use a developer comprising an electrically insulating liquid and a finely divided toner dispersed therein, and dry developing processes, such as the cascade process, fur brush process, magnetic brush process and powder-cloud process, in which a finely divider toner prepared by dispersing a coloring agent in a natural or synthetic resin is used singly or admixed with a solid carrier. The toners useful for such processes are charged positively or negatively in accordance with the polarity of the latent electrostatic image to be developed.
The toner can be made to retain electric charges by utilizing the triboelectric properties of the resin component of the toner, but since the toner is not highly chargeable by this method, the toner image obtained by development is prone to fogging and in turn to being obscure. To give the desired triboelectric properties to the toner, dyes and pigments for affording enhanced chargeability and further more charge control agents (triboelectrification control agents) are added to the toner. Presently used in the art for this purpose are oil-soluble nigrosine dyes for positively charging toners as disclosed in Published Examined Japanese Patent Application No. 2427/1966, and metal-containing complex dyes for negatively charging toners as disclosed in Published Examined Japanese Patent Application No. 26478/1970.
However, such dyes and pigments generally have low compatibility with the resin component of the toner, and are therefore difficult to disperse uniformly in the toner and tend to permit uneven charging, with the result that fog occurs in the developed toner image to obscure the image. Furthermore, even when the developer exhibits satisfactory developing characteristics in the initial stage of use, particles will collapse owing to uneven particle sizes or to the low compatability of the dye or pigment with the resin component, consequently forming fine particles consisting only of the dye or pigment. The toner will then scatter about markedly, staining the interior of the copying machine and contaminating the carrier so as to lower the ability of the developer to perform in the desired manner. Thus, the aforesaid use of such a dye or pigment involves many drawbacks.
Additionally, one of the substantial drawbacks of conventional dyes or pigments for imparting chargeability is that they are themselves color materials. This is in conflict with the basic requirement that chargeability imparting agents which are colorless or have a pale color that can be regarded as substantially colorless must be used for toners having a specific color. Published Unexamined Japanese Patent Application No. 127726/1978 (and correspondingly U.S. Pat. No. 4,206,064) discloses a metal complex of salicylic acid or alkylsalicylic acid as a material fulfilling the aforesaid basic requirement, but this material objectionably has low compatibility with the resin component of the toner.